1. Field of Invention
This invention concerns an LED device and a method by which it is produced. More specifically, it concerns an LED device used as a light source in display equipment, lighting equipment, and so on, and its method of production.
2. Description of Related Art
LED devices formed by bonding LED chips to exoergic members have been used as light sources in display equipment, lighting equipment, and so on in recent years; in these LED devices, a silicon resin or other resin is commonly used as a bonding material to bond the LED chips to exoergic members made of aluminum nitride (AlN), silicon carbide (SiC), Copper (Cu), or aluminum (Al), for example, or to lighting fixtures that function as exoergic members.
There is the problem, however, that because the resin used as a bonding material that forms the bonds between the LED chips and the exoergic members have inadequate heat resistance, a heat-resistance temperature of 100° C. or less, for example, bonds in the LED device deteriorate due to the heat from the LED chips and film cracks occur. Further, the heat generated by the LED chips in the LED device is not conducted across the bonds, and so the desired exoergic properties cannot be achieved, and this has a deleterious effect on increased brightness.
Therefore, it has been proposed that a eutectic alloy, such as Au—Sn alloy (gold-tin alloy), be used instead of resin as the bonding material between the LED chip and the exoergic member (see, Japanese Pre-grant Patent Publication 2004-134797).
In Japanese Pre-grant Patent Publication 2004-134797, as shown in FIG. 11, an Au (gold) layer 51 is formed over the full upper surface of the exoergic member 11 (the upper surface in FIG. 11), a bond comprising an alloy layer 52 is formed on that Au layer 51 by means of a bonding material that comprises an eutectic alloy, such as an Au—Sn alloy, and the LED device 12 is bonded.
In the example shown in FIG. 11, the LED device 12 is produced by forming a nitride semiconductor layer by stacking an n-type semiconductor layer 14A, a light-emitting layer 14B and a p-type semiconductor layer 14C in that order on a sapphire substrate 13.
In testing by the present inventors, however, the problem was revealed that, when bonds are formed using an Au—Sn alloy layer as the bonding material on an exoergic member 11 on which an Au layer 51 is formed, metal diffusion occurs in the heat treatment process to bond the LED device 12, diffusion of tin atoms of the Au—Sn alloy layer into the Au layer 51 causes reduction of the bonding strength between the LED device 12 and the exoergic member 11, and peeling occurs.